The invention relates to a method for automatic shutdown of an internal combustion engine in a motor vehicle, in particular in a motor vehicle having an automatic transmission, by way of a start-stop unit automatically switching-off the internal combustion engine when the vehicle is braked to a stop and is held at the stop for a predetermined time interval by pressing the brake pedal.
At the present time, internal combustion engines are usually shut down manually by the driver using an ignition key. One exception is a method presented in DE 100 23 331 A1, where instead of the ignition key, the brake pedal position and/or the brake pedal pressure is analyzed. The shutdown operation of the internal combustion engine is initiated when, after the vehicle reaches a standstill (stop), the brake pedal is operated more strongly in the position in which it has already been operated. One disadvantage of such a method is that only the vehicle driver is responsible for the shutdown of the internal combustion engine. Analyses of today's driving performance have shown that despite an increased environmental consciousness and rising fuel prices, manual shutdown of the internal combustion engine, e.g., at traffic lights is rarely done independently.
To reduce fuel consumption and pollution emissions, methods and systems are currently being developed (and to some extent have already been implemented) in which the internal combustion engine of a motor vehicle is automatically shut down under certain conditions and/or when predetermined shutdown conditions prevail and the engine is automatically started again when predetermined startup conditions prevail. Such methods and systems and/or stop-start devices are suitable in particular for city traffic to reduce fuel consumption. This is because in city traffic a vehicle will often come to a standstill at traffic lights or because of traffic, and operation of the internal combustion engine is not necessary then.
For example, a device which causes a shutdown and/or a renewed startup of the internal combustion engine depending on various conditions is known from EP 0 158 605 B1. One condition for initiating an automatic shutdown procedure is, for example, that the vehicle speed must be below a limiting value for a certain period of time before the internal combustion engine is automatically shut down.
One disadvantage of such methods and devices is that the current traffic situation cannot be taken into account. Consequently, the internal combustion engine is also shut down in situations in which the driver does not desire to do so for comfort reasons. For example, it would not be desirable to have automatic shutdown of the internal combustion engine at a turn lane or at a stop sign, where there is the option of continuing to drive immediately. In particular in the case of vehicles with automatic transmissions, under the prerequisite that the internal combustion engine is automatically shut down in braking to a standstill, the driver cannot prevent an automatic shutdown operation. If an inexpensive pinion starter is used as a starting system, then a lane change, i.e., starting the internal combustion engine while the vehicle is moving is impossible or is associated with a loss of convenience because the pinion starter can, in principle, make a lane change again only when the internal combustion engine is completely shut down. This also results in longer starting times under some circumstances.
To overcome this problem, methods and systems in which the driver can prevent an automatic shutdown are already known. EP 1 469 195 B1 thus discloses a method for automatic shutdown of an internal combustion engine in a vehicle in which the driver can prevent the automatic shutdown operation within a predetermined interval of time after reaching a standstill. For example, the automatic shutdown operation is not initiated when the driver steps on the brake pedal to a greater extent within the predetermined interval of time after reaching a standstill.
The object of the invention is to provide an alternative method for automatic shutdown of an internal combustion engine in a vehicle with or without an automatic transmission, to enable the driver to prevent the automatic shutdown operation in a simple and intuitive manner when decelerating the vehicle to shutdown.
This and other objects are achieved by a method according to the invention for automatic shutdown of an internal combustion engine in a motor vehicle (preferably in a motor vehicle having an automatic transmission) by way of a start-stop device. The method is, in principle, designed so that the internal combustion engine shuts down automatically when the vehicle is decelerated to a standstill (in addition to the other shutdown conditions, which are predetermined and have been met) and has been kept at a standstill by operation of the brake pedal for a predetermined interval of time. Within the predetermined interval of time after reaching a standstill, the driver is given an opportunity to prevent the automatic shutdown. The automatic shutdown should be prevented if the driver recognizes that continued driving is directly imminent.
In contrast with the prior art cited above, the present invention is characterized in that the automatic shutdown operation is not suppressed as soon as the driver depresses the brake pedal fully, but instead only when he has released it again at least somewhat after depressing it fully, i.e., instead of assessing the pressure buildup, the torque buildup, or the brake pedal distance traveled when the brake pedal is fully depressed as being the trigger for preventing the automatic shutdown operation of the internal combustion engine, only the subsequent pressure buildup, torque buildup or the brake pedal distance traveled in the subsequent release of the brake is assessed as being this trigger. This should prevent the automatic shutdown operation from already being suppressed when the driver only inadvertently depresses the brake pedal or his foot passes over it in deceleration to a standstill and the driver by no means intends to prevent the shutdown operation. Only the release of the brake pedal from the fully depressed state is evaluated as being a command to prevent the automatic shutdown operation.
This method is advantageous in particular for vehicles having automatic transmissions because the driver usually leaves the gearshift lever in the normal position during a vehicle standstill and there is no clutch pedal that could be interpreted with regard to the driver's intent. The “automatic transmission” concept includes, in addition to the traditional automatic transmissions, all the at least partially automated transmissions, including double-clutch transmissions (transmissions with and without transducers, EGS, SMG). However, this method may also be used in vehicles having a manual transmission. The start-stop device may be, for example, an independent control unit or may be integrated into the engine control unit.
Automatic shutdown of the internal combustion engine is advantageously prevented only when the brake pedal is released again after having been depressed fully at least by a predetermined amount. For example, the brake pedal position, the brake torque that has built up, or the braking force generated may be analyzed. Accordingly, automatic shutdown of the internal combustion engine is interrupted only when the brake pedal, after being fully depressed, is released until reaching the original actuated brake pedal position prior to the increased depression and/or until reaching the original braking force or the original braking torque prior to the increased depression. It is thus possible to ensure that the driver's intent to prevent the automatic shutdown operation will be reliably detected.
The driver of the vehicle may advantageously be informed by way of a display element as soon as he is able to prevent automatic shutdown of the internal combustion engine. If the predetermined operating conditions are met, an LED lights up, for example, signaling to the driver that the internal combustion engine will soon be shut down by the stop-start unit. As a display element, however, loudspeakers for an acoustic element or other elements for visual or haptic signals may also be used. Starting at this point-in-time the driver of the vehicle is able to prevent the internal combustion engine from being shut down.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.